The reelection of Ronald Reagan and concern about increased repression of blacks in South Africa led American black leaders to revive some of their old civil rights protest tactics from the 1960s and apply them to a new civil rights struggle, organizers of recent demonstrations outside the South African Embassy said yesterday.

While the embassy protests continued -- Rep. Ronald Dellums (D-Calif.), D.C. Council member Hilda Mason (D-Statehood) and United Automobile Workers Vice President Marc Stepp brought the number of arrests to 10 late yesterday -- leaders of the "Free South Africa Movement" announced plans to widen the anti-apartheid campaign Monday by holding similar demonstrations at South Africa's 13 consulates in this country.

The anti-apartheid movement, in the space of a few weeks, appears to have galvanized black support like no other social issue since the civil rights movement of 20 years ago, black leaders said. Long a concern, the decision to escalate the opposition to the South African policy of apartheid, which separates the races, can be traced to events both here and abroad.

The defeat in the last session of Congress of legislation to bar U.S. companies from investing in South Africa did not sit well with black legislators, while a challenge to fight his country's oppression of blacks, issued by Nobel Peace Prize winner Bishop Desmond Tutu, was taken very much to heart.

The protest was launched Nov. 21 when D.C. Del. Walter E. Fauntroy and two other black leaders were arrested after a sit-in at the embassy. Black members of Congress, District of Columbia officials, several labor union officials and well-known entertainment celebrities and athletes such as Harry Belafonte and Arthur Ashe have since joined protesters outside the Massachusetts Avenue NW embassy. The Rev. Jesse Jackson, who said during his campaign for the Democratic presidential nomination that the United States is South Africa's number one trading partner, expects to be there soon, too.

"I'm coming," Jackson said yesterday, calling the embassy demonstrations the highest level of black American protest aimed at the South African government.

Black exploitation, according to demonstrators, has increased under the Reagan administration's policy of "constructive engagement," a term coined early in Reagan's first term that advocates a more piecemeal approach in seeking human rights reforms in that country.

The Reagan administration, while calling apartheid abhorrent, argues that the way to seek improvements is not by treating South Africa as a pariah but by improving relations and urging reforms over a longer period of time.

But with the continued repression of 22 million blacks who account for 73 percent of South Africa's population, black leaders say the time for reform is now. They also complain that under "constructive engagement" the situation for South African blacks has correspondingly worsened, and they cite government retaliation after an anti-apartheid strike earlier this month.

"We saw that the oppression directly intensified as a result of the election of Ronald Reagan," said Randall Robinson, executive director of TransAfrica, a lobbying group for black issues that helped organize the embassy protests. "It was almost pegged to the reelection. All the black township invasions intensified, the killings."

Choosing sit-ins and other demonstrations to protest apartheid abroad, he said, is also a way of paying homage to the fight waged by U.S. blacks against oppression at home.

Fauntroy, president of the Black Leadership Round Table, said he and TransAfrica officials first discussed the idea of demonstrating at the embassy last month and began laying actual plans for the protest about two weeks ago, after the Nov. 6 reelection of Reagan and Sen. Jesse Helms (R-N.C.).

"This made it very clear to us that traditional means of influencing public policy are not likely to work in the next four years," Fauntroy said.

The embassy protests, according to organizers, have drawn widespread support from individuals who say they want to get involved. In terms of civil disobedience, they suggest, the 1980s may start to look like the 1960s.

"Everybody wants to get arrested . . . this may go on in Washington for quite awhile," said Fauntroy, who predicted that similar protests will be needed on behalf of the poor, student education programs and care for the elderly. "But our purpose at this point is not to jam the jails but to raise the consciousness of blacks and whites."

Fauntroy, who marched with Martin Luther King Jr. during civil rights protests, has been in jail before. But spending the night behind bars here, in a city where he is one of the top local political leaders, was "a first."

He and most of the others arrested have deliberately chosen to spend the night in jail prior to their arraignment, asking that they be treated no differently than other inmates.

That means, Fauntroy said, "I had no mattress. I had to sleep on a flat steel bunk, no blanket, no sheets."

For Rep. John Conyers Jr. (D-Mich.), arrested Tuesday, the decision to take part in his "first" protest demonstration and to spend a night in jail was "quite a liberating experience."

One of the founders of the Congressional Black Caucus, Conyers said Bishop Tutu's award "gave people new hope -- and we were also looking for a strategy to begin our second term of office under this president."

Leaders of the embassy protest voice concern that cheap black wages in South Africa have resulted in a "slave labor market" that is increasingly attractive to American corporations. And they blame the Reagan administration for the defeat last session of the Gray Amendment, a measure that would amend the Export Adjustment Act to prevent U.S. companies from investing in South Africa. The legislation passed the House but was rejected by the Republican-controlled Senate.

Black support for this and other measures fell on deaf ears, according to Robinson. He called recent meetings with Reagan's top foreign policymakers, including Secretary of State George Shultz, "absolutely, fundamentally useless."

The embassy protests were criticized Tuesday by South African Ambassador Bernardus Fourie, who compared them to the takeover of the U.S. Embassy in Iran.

A White House spokesman yesterday rebuked Fourie for comparing a peaceful sit-in to the 1979 seizure of the American Embassy in Iran.

In an interview with The Washington Post yesterday, Fourie said his earlier remarks were not intended to make such a comparison. He praised the Reagan administration for "its full support to protect the embassy."

Yesterday's demonstration here drew more than 100 protesters. At about 4:30 p.m., Dellums, Mason and Stepp were escorted by D.C. police to the steps of the embassy's east entrance, where they asked to speak to the ambassador.

After singing a chorus of "We Shall Overcome" and after refusing police orders to leave the premises, the three were arrested, searched and handcuffed and placed in two waiting police cruisers. Dellums and Stepp chose to spend the night at D.C. Central Cellblock while Mason was released.

"We have the right and responsibility to challenge what we don't believe," Dellums said shortly before his arrest. "Like the '60s, this is another movement when blacks are being called upon to be the conscience of this country."